feat(ui): batch of UI polish tweaks

- admin dashboard "Users" count excludes robots (CountUsers, humans only)
- lobby finished-game delete reveal: background matches header/tab-bar (--bg-elev)
- mobile: swipe up on the zoom-out board (no staged tiles) shuffles the rack
- lobby: status icons -25%, game-row top/bottom padding halved
- toast: info tier drifts up ~a tab-bar height while fading over 2s and dismisses
  on tap; error tier unchanged
- game: confirm-move button stays pinned at the right edge; rack tiles shrink to
  fit so a full rack never overflows onto it
- telegram: a successful invite-link redeem shows a welcome window pointing at the bot
- settings: remove the grid-lines toggle; the board is always a gapless checkerboard
- settings/comms hubs: the selected tab highlight wraps icon + label as a pill

Docs: UI_DESIGN (toast, board surface, selected tab), PLAN; e2e updated for the
removed grid-lines toggle.

ui/src/App.svelte

@@ -7,6 +7,7 @@
   import { insideTelegram, telegramBackButton } from './lib/telegram';
   import Toast from './components/Toast.svelte';
   import StaleInviteModal from './components/StaleInviteModal.svelte';
+  import WelcomeRedeemModal from './components/WelcomeRedeemModal.svelte';
   import Login from './screens/Login.svelte';
   import Lobby from './screens/Lobby.svelte';
   import NewGame from './screens/NewGame.svelte';
@@ -110,6 +111,7 @@
 
 <Toast />
 <StaleInviteModal />
+<WelcomeRedeemModal />
 
 <style>
   .splash {